Portable drafting device

ABSTRACT

A lightweight drafting device comprises a ferrous board and a magnetized roller which acts as a paper holder and guide means for a drafting element. The strong magnetic attraction between the board and roller ensure a fixed relation between the paper and drafting element, and maintains parallelism between drawn lines. The device is readily transportable and is operable in any convenient attitude.

United States Patent Baker [451 June 27, 1972 [54] PORTABLE DRAFTING DEVICE [72] Inventor: Allister L. Baker, Denville, NJ.

[73] Assignee: Keultel & Esser Company, Morristown,

[22] Filed: March 9, 1971 211 App1.No.: 122,406

[52] US. Cl. ..33/l09, 33/DIG. l [51] Int. Cl. [58] Field of Search ..33/DIG l, 109, 76

[56] References Cited UNITED STATES PATENTS 2,360,911 10/1944 Tress et a1 ..33/109 2,689,404 9/1954 Norman ..33/109 3,122,840 3/1964 Karsters .,33/DlG.1

Primary Examiner-Leonard Forman Assistant Examiner-Char1es E. Phillips Attorney-J. Russell Juten, Peter F. Willig, Lionel N. White and Milford A. J uten [57] ABSTRACT A lightweight drafting device comprises a ferrous board and a magnetized roller which acts as a paper holder and guide means for a drafting element. The strong magnetic attraction between the board and roller ensure a fixed relation between the paper and drafting element, and maintains parallelism between drawn lines. The device is readily transportable and is operable in any convenient attitude. I

7 Claims, 4 Drawing Figures PATENTEDJum I972 1N VENTOR ALLISTER L.BAKER MM.W

ATTORNEY BACKGROUND Drafting machines broadly preferred in the field of engineering drawing are generally of a type which provides vertical and horizontal straightedges associated with appropriate mechanics which afford such straightedges a wide range of movement in two orthogonal degrees of freedom over the face of a drawing surface. Such a drafting machine is described in U.S. Pat. No. 3,279,073.

While such drafting machines are noted for their ease of operation and excellent maintenance of parallelism in drawn lines, they are by their very nature and size suitable only for relatively permanent installation in offices and drafting rooms. A need has existed for some time, therefore, for an engineering drafting tool which could be readily transported, yet which would be capable of retaining the accuracy of orthogonal motion characteristic of the larger drafting machines.

An attempt to provide a portable drafting device has been described in US. Pat. No. 3,016,614 and generally comprises the use of mechanical restraints such as wires and flanged wheels as means to reduce the notorious instability of earlier mobile drafting instruments, such as rolling parallel rulers and the like. The described device has proven not entirely satisfactory, however, due to a continued tendency to yawing with resulting loss in parallelism between drawn lines.

The drafting device according to the present invention'employs a magnetized roller which is strongly retained by magnetic attraction in close association with a ferrous drafting board. The force of the magnetic field generated by the magnetic elements of the roller effectively prevents movement of the roller in any direction but that transverse to the axis of the roller, i.e., a straight and true rolling movement of the roller guide element is established regardless of the attitude of the drafting board.

The present drafting device further comprises a yoke element which overlies the roller, engaging the surface of the latter at internal concave bearing faces by means of which the yoke can readily ride with the rolling movement of the roller or slide axially upon the circumferential surface of the roller. The yoke member is thereby afforded two precisely orthogonal degrees of movement. Affixed to the yoke element is a line guide member, such as a drafting triangle or the like, which comprises two orthogonally disposed straightedges, one of which is parallel to the axis of the roller element engaging faces of the yoke member. The straightedges are thus adapted to respectively maintain parallelism regardless of the movement of the line guide element upon the drafting surface.

The magnetic attraction between the drafting device roller element and the ferrous drafting board serves an additional practical function. In the normal manner of use of the device a sheet of drawing paper or similar drafting medium overlays the board element and is retained in a fixed relation to the board element by the magnetized roller element positioned upon the sheet. This fixed relation and disposition between the board, paper, and roller element establish a base line for the drawing which remains true throughout the operation of the drafting device. In the event that the drafting device is disassembled for transportation, as in an engineers brief case, the drawing base line may be later quickly reestablished and retained throughout the further use of the drafting device. The use of tapes and tracks are additionally obviated, thereby providing a greater useful area on the drafting medium.

DRAWINGS In the accompanying drawings:

FIG. 1 is a plan view of a drafting device according to the present invention;

FIG. 2 is a partial section view of the drafting device taken at 2-2 ofFlG. 1;

FIG. 3 is a view, partially in section, of one embodiment of a magnetized roller member of the present invention; and

FIG. 4 is a view, partially in section, of a segment of another embodiment of the magnetized roller member of the present invention.

DESCRIPTION A preferred embodiment of the portable drafting device of the present invention is shown in FIG. 1 and generally comprises a drafting member assembly 10, a magnetic roller member 11 and a drafting board member 20. The drafting member assembly 10 comprises a yoke element 14 to which is rigidly attached a line guide element 16. Guide element 16 is preferably a transparent acrylic sheet having the form of a common drafting triangle. A major straightedge of the triangle may be conveniently marked in units of measure and serves as one of a pair of orthogonal lining guides. A slot 17 in the body of the triangle provides the second of the line guide straightedges which may be similarly marked in units of measure. A protractor segment 18 having indexing indicia (not shown) is mounted for rotation in a known manner at a circular cutout in the body of triangle element 16. Slots 19 provide finger access to assist in rotary movement of protractor element l8.

Roller member 11 comprises a cylindrical body 12 having magnetic elements 13 affixed axially at both ends of the body, thereby forming a magnetic rod or roller which is strongly attracted to any ferrous body. The construction of roller member 1 l is shown in greater detail in FIG. 3.

Drafting board member 20 is a generally rectangular sheet of steel or other ferrous material which is of sufficient thickness to provide a practical degree of rigidity. One edge of drafting board 20 is partially folded back upon itself to form a straightedge lip 21 which serves during operation of the drafting device as the primary baseline guide and additionally functions as a paper stop and alignment edge.

The operation of the drafting device of the present invention is apparent from FIG. 1. A sheet of paper or other drafting medium 15 is set upon the surface of board member 20 and is pushed into squared abutment along one edge with drafting board corner 33 (FIG. 2). After general orientation of the paper 15 upon board member 20, roller member I] is set upon the face of the paper in a position generally axially parallel to the baseline edge 31 of board lip 21. The magnetic attraction of roller member 11 to board 20 firmly affixes the paper in generally squared position upon the face of the board.

Yoke 14 of drafting member assembly 10 is then set upon roller 11, closely engaging the roller at internal faces 26, 26' of like radius of curvature to the surface of roller 11. The assembled combination 10, 11 is moved toward board lip 21 until yoke tail section 29 engages board lip 21 at baseline edge 31.

In the event that tail section 29 is not in contact with edge 31 along its entire length, sufficient force is applied to yoke 14 to overcome the magnetic attraction between the roller and the board member so that contact is made between the squaring edge 31 and yoke tail section 29 along the entire length of the latter. This squaring operation establishes a baseline between the paper 15 and the lining straightedges of triangle 16 which may be readily reestablished by a like operation even after intermittent disassembly of the drafting device.

The assembled drafting device provides a truly orthogonal movement of the line guide element 16 and its associated straightedges. Horizontal movement is established through the rolling action of member 1 1 over the face of the board 20 and drafting sheet 15 while vertical movement is established by the axial sliding of yoke 14 on the face of roller member 11. Representative movement of the drafting member assembly 10 is shown at 10'.

For convenience in the establishment of various angles with respect to the orthogonal straightedges of drafting member 10, protractor member 18 is inset into a circular guide in the body of triangle 16. The protractor element is readily rotatable within the circular guide as indicated in phantom at 18'.

Referring to FIG. 2 of the drawing, the drafting device is seen in preliminary squared baseline adjustment with the yoke tail section 29 in abutment with the squaring edge 31 of board lip 21. A preferred construction of the device is also seen wherein yoke 14 is conveniently formed by extrusion from a non-ferrous material such as aluminum or plastic. The inner surface of yoke 14 comprises two inward protruding ridges, the surfaces 26, 26 of which conform precisely in concave curvature to the circumferential curvature of the roller member as represented by the cylindrical tube roller body 12. The concave surfaces 26, 26' present a low-friction bearing surface such as can readily be obtained by a layer of polytetrafluoroethylene bearing material or any of a number of commercially available bake-on" dry lubricants comprising, for example, mixtures of silicon, graphite, and epoxy resin binder.

A lip section 28 is conveniently included in the extruded form of yoke 14 and includes a channel generally parallel to the baseline alignment surface of yoke tail section 29 by means of which guideline element 16 may conveniently be affixed to yoke 14. The joint between yoke 14 and guideline element 16 may be permanently achieved through the use of adhesive and press forming, or provision (not shown) may be included for removable attachment of guideline element 16 in order to provide interchangeability of various shapes of element 16.

The construction of a preferred embodiment of roller 11 is shown in FIG. 3 and comprises a cylindrical, tubular roller body 12, preferably of non-ferrous material such as aluminum or plastic. At each end of body 12 there is inserted a soft iron bushing 37 having a center hole through which a non-ferrous threaded rod 36 is inserted. Arranged upon the extending ends of rod 36 are center-bored discs, or rings 13 of permanently magnetized material alternating with center-bored soft iron discs, or rings 35 which form pole pieces in the magnet assembly. Any desired number of elements in this alternating structure combination may be included and the assembly is finally completed by a tapped nut element 39, preferably of soft iron to act as the final pole piece of the assembly.

Magnetized disc elements of the present construction are commercially available and are preferably formed of pre magnetized ceramic composition or other permanently magnetized material, for example as described in U.S. Pat. No. 2,762,777. The pre-magnetized discs are characteristically polarized in their axial direction and present a definite North pole at one face and South pole at the opposite face. The pole dispositions are specifically noted in FIG. 3 where the preferred arrangement is depicted as the alternation of N-S elements 13 and S-N elements 13' along the length of roller 11. This arrangement with the further inclusion of alternating soft iron ring discs 35 which act as pole pieces for the respective pairs 13, 13' of the magnetized discs result in a strong, closely-formed magnetic field along the whole surface of the magnet sections of roller 11. A final operation in the construction of roller 11 comprises the centerless surface grinding of the entire member to achieve parallel surfaces to insure true rolling movement of the drafting device when in operation. During this grinding operation the radius of curvature of the surface of roller 11 may be conveniently adjusted to precisely conform with the radius of curvature of surfaces 26, 26 of yoke member 14 as previously noted.

Another embodiment of a roller member is shown in FIG. 4 and comprises a solid cylindrical rod body element 41 of nonferrous metal or plastic to the ends of which are adhered, by epoxy adhesive composition or the like, alternating discs of soft iron 35 and magnetized ceramic 13 in the manner described previously. The N-S discs 13 are similarly arranged in alternating sequence with S-N discs 13 with intervening soft iron pole pieces 35 to obtain the strong, directed magnetic field as earlier described. Yet another embodiment in the construction of the magnetized roller may include the use of a combination of a central alignment rod and a tubular body section as in FIG. 3 with the adhesive junctures employed in the embodiment of FIG. 4. In any event, the final operation of centerless gnndrng to achieve true rolllng surfaces and close mating with the curvature of surfaces 26, 26' of yoke 14 completes the construction of the magnetized roller.

The drafting device of the present invention has been found to provide in its movement and manner of handling, a convenient and faithful reproduction of the larger, premanentlyaffixed beam-type drafting machines. Besides providing a handy tool for the traveling design engineer, the drafting device represents a particularly useful training apparatus for engineering students due to the faithful duplication of commercial drafting machines in all its movements. Thus the invention provides a low-cost, readily-portable replica of more expensive drafting machines and provides students with an early opportunity to become well acquainted with the manner of operation of apparatus which they would not ordinarily encounter until their employment years.

What is claimed is:

l. A portable drafting device comprising, in combination:

a. a drafiing board member comprising a substantially flat magnetically attractable working surface;

a magnetized cylindrical roller member in magnetic engagement with said working surface; and

c. a line guide member comprising a yoke element encompassing a substantial segment of the circumferential surface of said roller member, said yoke element including bearing means engaging said roller surface at a plurality of points defining at least one roller surface area which intersects a plane which is perpendicular to said board member and contains the axis of the roller, thereby establishing two orthogonal degrees of freedom for movement of said line guide member with respect to said board member.

2. A device according to claim 1 wherein said drafting board member includes an upstanding wall segment presenting abutment surface portions respectively providing bases of alignment between said board and a paper sheet overlaying said board, and between said board and said roller member.

3. A device according to claim 2 wherein said abutment surface portions present substantially parallel base lines of reference for alignment of said roller member and at least one straight edge of a sheet of paper overlaying said board.

4. A device according to claim 1 wherein said yoke element bearing means comprises a planoconcave surface having a radius of curvature equal to the radius of curvature of the curvature of the circumferential surface of said roller member.

5. A device according to claim 4 wherein said yoke element includes a substantially vertically disposed surface portion forming an abutment edge which is substantially parallel to the axis of curvature of said plano-concave bearing surface.

6. A device according to claim 1 wherein said roller member comprises a plurality of magnetized cylindrical segments axially affixed to a cylindrical body and of like circumference thereto, said magnetized segments each exhibiting a north and a south magnetic pole.

7. A device according to claim 1 wherein said drafting board member comprises a substantially rectangular rigid flat plate of ferro-metallic material, said plate having at least one straight edge and having a portion adjacent said straight edge folded back along a line parallel to said straight edge to yield an upstanding wall segment forming an acute angle with the remaining portion of said plate. 

1. A portable drafting device comprising, in combination: a. a drafting board member comprising a substantially flat magnetically attractable working surface; b. a magnetized cylindrical roller member in magnetic engagement with said working surface; and c. a line guide member comprising a yoke element encompassing a substantial segment of the circumferential surface of said roller member, said yoke element including bearing means engaging said roller surface at a plurality of points defining at least one roller surface area which intersects a plane which is perpendicular to said board member and contains the axis of the roller, thereby establishing two orthogonal degrees of freedom for movement of said line guide member with respect to said board member.
 2. A device according to claim 1 wherein said drafting board member includes an upstanding wall segment presenting abutment surface portions respectively providing bases of alignment between said board and a paper sheet overlaying said board, and between said board and said roller member.
 3. A device according to claim 2 wherein said abutment surface portions present substantially parallel base lines of reference for alignment of said roller member and at least one straight edge of a sheet of paper overlaying said board.
 4. A device according to claim 1 wherein said yoke element bearing means comprises a plano-concave surface having a radius of curvature equal to the radius of curvature of the curvature of the circumferential surface of said roller member.
 5. A device according to claim 4 wherein said yoke element includes a substantially vertically disposed surface portion forming an abutment edge which is substantially parallel to the axis of curvature of said plano-concave bearing surface.
 6. A device according to claim 1 wherein said roller member comprises a plurality of magnetized cylindrical segments axially affixed to a cylindrical body and of like circumference thereto, said magnetized segments each exhibiting a north and a south magnetic pole.
 7. A device according to claim 1 wherein said drafting board member comprises a substantially rectangular rigid flat plate of ferro-metallic material, said plate having at least one straight edge and having a portion adjacent said straight edge folded back along a line parallel to said straight edge to yield an upstanding wall segment forming an acute angle with the remaining portion of said plate. 